In many outdoor scenarios, the wireless multipath channel exhibits multipath components whose delays are longer than the Cyclic Prefix (CP) used in multi-carrier systems such as orthogonal frequency-division multiplexing (OFDM). The aforementioned system will be referred to as an “insufficient CP system”. In insufficient CP systems, the multipath components with delays longer than the CP lead to two types of interference, namely Inter-Symbol Interference (ISI) and Inter-Carrier Interference (ICI). This means that the samples of the current symbol are interfered by samples of the previous symbol (ISI), but they also exhibit self-interference, i.e. each subcarrier leaks power on the adjacent subcarriers (ICI). ISI and ICI corrupt the transmitted signal and therefore affect the performance of pilot-based channel estimators, e.g. such as used in LTE systems and also that of the equalization. Since the pilots used for channel estimation become corrupted by interference, the original set of pilots becomes insufficient to accurately resolve the channel multipath components. Since data subcarriers exhibit interference from adjacent subcarriers and also from delayed previous symbols, traditional equalizers unaware of these effects become highly error-prone.
It may be desirable to improve channel estimation in wireless communication networks, in particular in insufficient CP systems.